Possible Bug in HG

I was playing as the Persians last night, and I attacked an Athenian city across the Hellespont using ships. My units were beaten, but then a much larger force of Athenian soldiers actually walked across the Hellespont and attacked my other units which were still waiting to be transported.

There are some points on the map where one of two indicators show there's a passage for your land-based units across water: One is a wooden construction like the one you can see right next to Pella. The other one is rather unremarkable and represents passage by two fire bowls on each side of the coastline. One of the latter is present near Abydos - the Hellespont was an important land route from Greece to Persia using pontoon bridges.

Anyway, that was the biggest battle I have seen in this game, but I managed to rout the enemy with only 50% casualties of my own after calling in troops from all over the Persian Empire. I will have to build up the army again before I cross the Hellespont, though. I could take the risk of crossing and taking the three cities there, as the enemy is weak there now, but I might wait for a while - but this gives them time to build up their troops, too. Choices, choices.....